Victor Forge
The cardiac muscle is a striated, branched muscle that must contract with enough force and blood to supply the metabolic demands of the entire body. This is known as cardiac output. The concentration of calcium in the myocyte determines how much force is generated with each contraction. Cardiac muscle cells can increase contractility through beta-1 adrenergic receptors on the surface with a Gs G-protein. When stimulated by either the sympathetic nervous system or beta-1 agonist drugs, the Gs activate the enzyme adenylyl cyclase, which converts ATP to cAMP. Intracellular cAMP increases the activity of protein kinase A (PKA), which then phosphorylate calcium channels permitting more calcium to enter the cell, leading to increased contraction.
| Characteristics | Values |
|---|---|
| Stimulation type | Electrical |
| Stimulation trigger | Cardiac action potential |
| Stimulation result | Release of calcium from the cell's internal calcium store |
| Calcium store name | Sarcoplasmic reticulum (SR) |
| Calcium store size | Smaller and less elaborate |
| Calcium ion storage | Stores less calcium ions |
| Calcium ion source | Extracellular |
| Calcium ion entry | Through T-tubules |
| Calcium ion release | Triggered by extracellular calcium ions |
| Muscle cell connection | Electrically connected through gap junctions |
| Stimulation spread | Waves of electrical stimuli pass around the heart from cell to cell |
| Muscle fibre stimulation | Causes a wave of depolarisation to pass down the T-tubule |
| Calcium ion movement | Pumped back up into the SR to lower calcium ion concentration in the sarcoplasm |
| Muscle state | Relaxed (turned off contraction) |
| Cardiovascular response | Heart rate and blood pressure changes |
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What You'll Learn
- Electrical stimulation triggers the release of calcium from the cell's internal calcium store
- Cardiac muscle cells depend on extracellular calcium ions
- Cardiac muscle cells are electrically connected through gap junctions
- Mechanical pressure stimulation of skeletal muscles can induce reflex changes in heart rate and blood pressure
- Excitation of group III and IV afferent fibres
Electrical stimulation triggers the release of calcium from the cell's internal calcium store
The SR is a membrane system derived from the endoplasmic reticulum. It is smaller and less elaborate than the endoplasmic reticulum, and stores fewer calcium ions. Cardiac muscle cells also depend on extracellular calcium ions, which enter through the T-tubules. These T-tubules lie next to the terminal cisternae of the SR. When the muscle fibre is stimulated, a wave of depolarisation passes down the T-tubule, triggering the release of calcium ions from the SR into the sarcoplasm. This release of calcium ions is essential for muscle contraction.
Cardiac muscle cells are electrically connected through gap junctions, allowing waves of electrical stimuli to pass around the heart from cell to cell. This ensures that the heart contracts in a coordinated manner.
After the release of calcium ions, calcium is pumped back up into the SR to lower the calcium ion concentration in the sarcoplasm and relax the muscle, turning off the contraction. This process is vital for maintaining the proper function of the heart and ensuring that it contracts and relaxes in a controlled manner.
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Cardiac muscle cells depend on extracellular calcium ions
The T-tubules lie next to the terminal cisternae of an internal membrane system derived from the endoplasmic reticulum, which is called the SR. This system is a store of calcium ions. Stimulation of the muscle fibre causes a wave of depolarisation to pass down the T-tubule, and the SR to release calcium ions into the sarcoplasm. Calcium is then pumped back up into the SR to lower the calcium ion concentration in the sarcoplasm, which relaxes the muscle and turns off contraction.
Cardiac muscle cells are electrically connected through gap junctions, so that waves of electrical stimuli pass around the heart from cell to cell. This allows for the coordinated contraction and relaxation of the heart muscle, which is essential for the pumping action of the heart. The T-tubules in cardiac muscle lie over the Z-line and are less numerous and wider than in other muscle types.
Overall, the entry of extracellular calcium ions through the T-tubules and the subsequent release of calcium ions from the SR is a critical step in the stimulation of cardiac muscle cells. This process initiates the contraction of the heart muscle, which is necessary for the heart to pump blood effectively throughout the body.
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Cardiac muscle cells are electrically connected through gap junctions
Electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum (SR). The SR is a store of calcium ions. When the muscle fibre is stimulated, a wave of depolarisation passes down the T-tubule, and the SR releases calcium ions into the sarcoplasm. This causes the muscle to contract. To relax the muscle, calcium is pumped back up into the SR to lower the calcium ion concentration in the sarcoplasm.
Cardiac muscle cells also depend on extracellular calcium ions, which enter through the T-tubules and trigger the release of calcium ions from the SR. The T-tubules in cardiac muscle are less numerous and wider than in other muscles, and they lie over the Z-line.
Cardiovascular responses to skin and muscle stimulation are mainly attributed to the excitation of group III and IV afferent fibres. Mechanical pressure stimulation of skeletal muscles can induce reflex changes in heart rate and blood pressure.
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Mechanical pressure stimulation of skeletal muscles can induce reflex changes in heart rate and blood pressure
Cardiac muscle cells are electrically connected through gap junctions, allowing waves of electrical stimuli to pass around the heart from cell to cell. This electrical stimulation triggers the release of calcium ions from the sarcoplasmic reticulum (SR), an internal membrane system that stores calcium ions. The SR is smaller and less elaborate in cardiac muscle cells, storing fewer calcium ions. These cells also depend on extracellular calcium ions, which enter through the T-tubules and further trigger the release of calcium ions from the SR.
The T-tubules lie next to the terminal cisternae of the SR and stimulation of the muscle fibre causes a wave of depolarisation to pass down the T-tubule, prompting the SR to release calcium ions into the sarcoplasm. To relax the muscle, calcium is pumped back up into the SR to lower the calcium ion concentration in the sarcoplasm. Cardiac muscle also contains T-tubules, but these are less numerous, wider, and lie over the Z-line.
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Excitation of group III and IV afferent fibres
Cardiac muscle stimulation occurs when electrical stimulation triggers the release of calcium from the cell's internal calcium store, known as the sarcoplasmic reticulum (SR). This process is essential for maintaining proper heart function. Cardiac muscle cells, or cardiomyocytes, are unique in that they possess T-tubules, which are membrane invaginations that facilitate rapid transmission of electrical signals. These T-tubules are crucial for coordinating the contraction of the heart muscle.
The T-tubules in cardiac muscle cells are wider and less numerous than those in skeletal muscle cells, and they lie over the Z-line. When an electrical stimulus reaches the T-tubules, it triggers the release of calcium ions from the SR. This release of calcium ions is essential for muscle contraction. The SR is smaller and less elaborate in cardiac muscle cells compared to skeletal muscle cells, and it stores fewer calcium ions. However, cardiac muscle cells also rely on extracellular calcium ions, which enter through the T-tubules and further contribute to muscle contraction.
The excitation of group III and IV afferent fibres plays a significant role in cardiovascular responses to skin and muscle stimulation. These fibres are sensitive to mechanical pressure stimulation and can induce reflex changes in heart rate and blood pressure. The exact neural mechanisms underlying this effect are not yet fully understood, but research has shown that stimulation of mechanoreceptors in skeletal muscles, such as contraction and stretch, elicits reflexive autonomic nervous system changes that impact cardiovascular control.
Cardiac muscle cells are electrically connected through gap junctions, allowing waves of electrical stimuli to pass from cell to cell. This coordinated electrical activity ensures the synchronised contraction of the heart muscle, which is vital for effective blood circulation. The excitation of group III and IV afferent fibres likely contributes to this process by modulating the electrical activity and contraction of cardiac muscle cells.
Furthermore, the excitation of these afferent fibres may influence the activity of cardiac autonomic nerves, which play a role in regulating heart rate responses. By understanding the role of group III and IV afferent fibres in cardiovascular control, researchers can gain insights into the complex neural mechanisms that underlie heart rate and blood pressure regulation during exercise or other physiological conditions.
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Frequently asked questions
Cardiac muscle stimulation is caused by electrical stimulation in the form of a cardiac action potential.
It triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum (SR).
The SR is smaller and less elaborate, and stores less calcium ions.
They depend on extracellular calcium ions, which enter through the T-tubules and trigger the release of calcium ions from the SR.
